All language subtitles for Lecture05 Scientific Secrets for Powerful Memory

Where are your memories stored?

In your brain, right? Of course. But where in your brain?

I know that the capital of Belgium is Brussels.

Where exactly is that information stored?

I remember very clearly the day that my daughter was born.

I remember walking around a hospital room watching her watch me
and then fall asleep at such a precious and important memory for me.

But where is it?

If you've ever pondered that question, you aren't alone.

Brain scientists have wanted an answer to this question
for about as long as there have been brain scientists

in Several of the previous four sessions have made comments
about the way that your brain implements memories.

In this session, we'll be considering this in more detail.

I'll be describing some experiments done with rats that suggest that
the entire brain is involved in encoding different aspects of memories.

Where are your memories? They're everywhere.

Ultimately, I'll argue that

to keep your memory functioning
well, you need to engage and promote the health of your entire brain.

In the second session, I talked about brain injured patients and how
damage to particular brain structures affected their memory abilities.

For instance,
we talked about patients who've suffered damage to the hippocampus,

a subcortical structure associated with many mental functions
without a functioning hippocampus.

These patients retain their ability to recall older memories.

Also, they retain their working memory.
Their short term memory remains fully intact.

What these patients have lost is the ability to take the information
in that short term memory

and transform it into more durable, long term memories.

Studies like this suggest a brain
that's organized in a very compartmentalized fashion.

Brain scientists often use the word modules to describe parts
of the brain that perform particular specific cognitive functions.

Given my stories about these particular studies,
it would be reasonable for you to infer

that only some areas of the brain are involved in storing
and recalling memories

for a few minutes.

I want to consider some research
that suggests the opposite that in fact, most, if not all, of

the brain is involved in normal, complex
memory processes, memory processes that you have in your everyday life.

These studies weren't conducted with humans, but with rats.

Carl Lashley was a young neuroscientist when he undertook this
research program that I'm going to tell you about.

His goal was simple.

He wanted to know where memories are stored in the brain.

He decided to work with rats.

Now a human brain and a rat brain are very different
from one another, of course, but there are many similarities.

If we actually could find the location
where memories are stored in the rat brain,

it would likely be easy
to figure out what the analogous place was in the human brain.

Lashley's experimental method with these rats was very straightforward.

You would have rats repeatedly run through a maze
searching for some food at the end of the path

until they got very good at doing that task.

That is, until they had formed a memory of the structure of the maze.

At that point, Lashley would perform a bit of brain surgery on the rats.

He would choose a particular location in the brain and cut it.

In so doing, reducing or eliminating its ability to do whatever it did.

Lashley repeated this many times with many rats systematically varying
where in the brain and how much brain tissue he would excise.

Lashley's prediction was that
he would eventually find some place in the rat

brain or places that,
if damaged, resulted in a loss of memory for the rats.

They would, after this very specific surgical damage to this area
of the brain that contains memories, be unable to navigate the maze.

If this area were responsible for memory and nothing else,
then you'd have a rat with what essentially would be retrograde amnesia.

It would be perfectly fine in every way, except no long term memories.

Well, this was Lashley's plan, but more than three years later,
he was still doing the same experiment

with really no greater idea
about where memories were, where they're stored than when he started.

It's worth taking a moment here

to thank the rats for their many sacrifices
for the sake of brain science and medical science in general.

Also, I should note that in studies like this, careful precautions
are taken to minimize any suffering by these creatures.

So after more than three years,
Lashley stepped back from his initial question

about the location of memories in the brain and made
what's become a classic graph on the vertical axis.

He plotted the amount of increased errors
made by rats after their surgeries on the horizontal axis.

He plotted the amount of brain damage caused, not the area of the brain
injury at all, just the size of the damaged area.

Lashley's graph showed a clear and consistent relation
between these two variables.

It doesn't seem to matter where you damage the rats brain at all.

For the maze running memory task.
What matters is how much of the brain is damaged.

Two things can be inferred from this finding.

First, there is no single memory storage area in the brain.

Lashley never found it because there doesn't seem to be one.

Second, there seem to be few,
if any, parts of the brain that are not involved in memory storage.

Where are rat maze memory stored everywhere.

This turns out to be true for humans as well as rats.

There's now a lot of good evidence
that information is stored to some extent all over your brain

in order to keep your memory functioning at an optimal level.

You need to maintain more than just your hippocampus.

The whole organ is involved.

The brain is one of the most vascular parts of our body,

with millions of capillaries
providing oxygen and fuel to each and every part of the brain.

Good circulation is also essential
to remove the waste products produced by the brain.

The brain consists of neurons which are very specialized types of cells,

but they are at the end of the day, Also, like other cells,
they need resources to live and even more to thrive.

It's often noted that we make all of the neurons
that we're going to have in the first few years of our lives.

That turns out not to be completely true, but mostly so.

We rarely generate new neurons in our central nervous system
into the brain where memories are processed.

Injury and damage to the brain often results
in lasting memory issues for this reason.

While entirely new neurons are rarely generated in the brain
during adulthood,

new connections between neurons are formed and destroyed all the time.

This is, in essence, how we learn.

It's a remarkable thing to contemplate, actually.

The sheer number of these connections changes that happen every day.

Every time we remember something.

So what do you think you can do to maintain or enhance your memory?

Take a particular vitamin, particular drug.

Do crossword puzzles.

Do some sort of Sudoku based mental exercise.

Actually, one of the simplest and most effective ways

to improve your memory, it turns out, isn't any of the mental techniques
that I've described up to this point in the course.

It's exercise. Physical exercise.

There have been a lot of studies on exercise
and the formation of new synapses in rats and other non-human animals.

When you compare rats who live a sedentary life
to those who run on an exercise wheel

with a spending a lot of time engaged in physical activity,
a wide range of differences show up.

The density of the neurons in the cerebellum,
that's an area associated with learning to perform particular actions.

This density increases the density of the dopamine receptors
in the brains.

In these rats also increases.

Exercise causes activation of the gene that produces
a protein associated with the growth of nerves called brain

derived neurotrophic factor.

This leads to the growth of tissues
that make those connections between neurons.

Those connections that are responsible for forming new memories.

In terms of research on rats.

The verdict is in.

Exercising produces
a brain with a more densely connected and active network of neurons.

Several studies have shown
that this improved neural network has behavioral consequences as well.

When it comes time for the rats to learn new information,
it's not just about increasing cell density.

These are actually smarter rats.

Human brains and rat brains are similar in many ways,
certainly at a molecular level.

But until recently, there were several reasons to resist
extending these conclusions to humans.

There are differences between humans and rats, such that exercise
might be less important for humans than for rats, for instance.

Another reason for concern is that most of these studies with rats
have, by design, considered extremes of activity.

The sedentary rats never ran on the exercise wheel,
whereas the active rats

ran on the exercise wheel for long periods of time
every day for their entire lives.

It might be that a little activity
would be enough to cause those observed changes.

For instance, or perhaps a lifetime of intense activity
is the only way to produce an achievable benefit.

Ongoing research
with rats has continued to explore these types of questions.

People who study humans have approached this topic
with great enthusiasm. However, based on those rat results.

There's reason to

expect something of interest to be found relating exercise
to brain performance in humans.

Some early studies compared sedentary
and athletic older adults and found what one might expect.

Active people tend to have higher levels of cognitive performance
according to a variety of measures, including measures of memory.

So exercise might promote good brain performance.

But there's another explanation here, if you think about it.

Perhaps people with high functioning brains are more likely to be active
than those with poorly functioning brains.

That is maybe the connection between brain function and exercise.

The causal connection runs in exactly the opposite direction.

What's needed here is a longitudinal study,
one in which people are recruited and then assigned randomly

to experimental conditions in which they're either urged
or not urged to engage in extra physical activity.

Brain fitness in these studies is assessed before and after the study.

If the additional exercise results in better brain function,
then the causal link can be established.

These studies are as you might imagine, hard to do.

They take years and they're actually quite intensive in terms of the
the research effort.

After the people are recruited
for the study, they need to be tracked and assessed on a regular basis.

Some participants might move away.

Some might drop out of the study.
Some assigned to the exercise conditions.

I choose not to perform the scheduled activities,
or perhaps they might become ill and not be able to.

As such, while some of these studies were promising,
none of them seemed to make a really clear

case by themselves for this connection
between exercise and brain performance.

Two researchers at the University of Illinois,
Stanley Holcomb, and Art Kramer,

made a major contribution several years ago
when they performed something called a meta analysis on this issue.

The method is basically to pull together data from many related studies
to see if they all tend to point in one direction or not.

But analysis is a bit like detective work.

It starts with identifying studies that are related
and then contacting researchers to obtain copies of their data.

The studies are all similar, but each is also different.

So a system for encoding those different factors has to be developed.

The results of a meta analysis, however, can be very powerful.

In essence, the findings are what one might have obtained
by conducting an absolutely enormous study

involving thousands of participants and dozens of study sites.

The conclusions that Kokum and Kramer reached were very intriguing.

The first thing to note is that there is indeed a significant positive
effect of exercise on mental function as we age.

The effects were larger for women than for men.

The effects were also largest for tests that tapped something called

executive function mental process
associated with decision making and cognitive control.

While the effects were largest there, there were substantial effects
where virtually every measure of mental function

that have been used in these kinds of studies.

No tests were done for memory specifically,
but many of the tests used in these various studies did require memory.

Given the wide range of tasks used, there's reason to be confident
that memory was better for the active than the sedentary groups here.

Another really interesting
finding emerged that provides a very specific prescription

for how much activity one should do for studies
in which participants engaged in less than 30 minutes of daily activity.

Positive, positive effects were present,
but they were much, much smaller

than those observed for 31 to 45 minutes of activity
or 46 to 60 minutes of activity.

It's worth noting that there was no clear advantage of 46
to 60 minutes, over 31 to 45 minutes.

In fact, the mean effect size was larger for that 31 to 45 minute group.

So how long does one need to be active each day to promote good brain
fitness?

The clear suggestion here is a bit longer than 30 minutes.

The meta analysis also considered the types of activities
that people engaged in.

Many different activities were included.

The the researchers who did the meta analysis grouped them into those
that promoted cardiovascular health

and those that promoted cardiovascular health,
along with strength training, including the strength training.

Training exhibited a clear advantage
in terms of the amount of improvement in brain function,

the duration of the interventions used in the individual studies
also varied widely, but effects could be seen even within a few months.

I like my brain functioning as well as it can,
so you'll see me out there running and walking a lot these days,

at least a few times each week.
I need to get back into the gym to lift some weights as well.

Apparently if you do the same then within a few months
your brain will be functioning better than it does even now.

All of this exercise talk might be making you a bit tired.

And from a memory standpoint, that's a good thing

because another key thing to do to enhance
your brain function is to sleep, perchance to dream.

Actually, the dreaming part isn't an option because dreaming seems to be
an important component of how we store memories.

The research on this topic
is something that remains a topic of some ongoing debate.

Even the nature of dreams,
I should say, is something that people continue to argue about.

The perspective that I find most compelling.

And so the one I'll be talking about in this session considers dreams
as simply a period of sleep during which our brains are very active.

We experience that activity in our largely unconscious state
and then try to make sense of it.

Sometimes an interesting story emerges
from our understanding of this activity.

Other times there are just bizarre sequences of ideas and images
that pass through our mind.

The one piece of this that I'll ask you to keep in mind for the moment
is that we often dream about things that happened

during the recent past.

If I saw an old friend at the supermarket for the first time
in a long time, he might show up in my next evening's dreams.

If we ride on

that scary new roller coaster,
then get ready for some excitement at bedtime.

With that in mind, let me take a step back and define dreams
from the perspective of a cognitive scientist.

As we fall asleep and slowly lose our consciousness,
our brains become less active for a while.

They never shut down completely. However, not. Not even close.

They produce rhythmic cycles of activity
over the course of about 90 minutes and then repeat that cycle.

As long as we continue to sleep.

First, we drift into a shallow sleep,
but that becomes deeper and then deeper still.

If you have an electroencephalogram, an EEG
attached to the scalp of a sleeper,

you can watch the waves of electrical activity grow slower, plateau
than slower still, then plateau in the deepest stages of sleep.

If you ever try to wake

someone while they're in this deepest stage of sleep,
they typically awake, confused and disoriented.

Only after a few minutes.

Will they be capable of reasoning
and having a sort of a good conversation again.

They're also typically quite irritable,
so the conversation might not be so pleasant.

Presuming that we don't wake the person
and allow them to continue sleeping.

The brain will begin to become more active.

Stepping back up through those stages of sleep.

Near the end of the 90 minute cycle,
the brain begins to emit very high frequency bursts of activity.

The eyes often twitch back and forth.

These rapid eye movements, REM's are the namesake of REM sleep.

Interestingly, the body itself becomes largely paralyzed
during these periods of REM sleep.

The connections between the spinal cord

and parts of the body that that cause body movements
become downregulate to the point that they're almost disconnected.

That's a good thing, since these bursts of activity
might otherwise cause jerky, violent movements.

If we let the sleeper continue sleeping.

This REM phase will last for about a minute, often less
before the sleep cycle begins anew.

The brain produces ever slower and slower rates of activity.

Descending into a deep sleep, then ascending again
until there's another burst of REM.

It's during this REM phase of sleep that dreaming occurs.

If you wake someone while they're in this REM phase, they will almost
always report that they were dreaming when you woke them in that moment.

They'll be able to tell you about the dream that was taking place,
but within minutes their memory of it will begin to fade.

This is an interesting memory phenomenon in itself.

Most people don't usually remember many of the details of their dreams.

Upon learning about this 90 minute cycle, most people are surprised
to learn that they even have as many dreams as they do.

If you sleep for seven and a half hours,
you will very likely have had five dreams.

Some people even claim that they don't dream,
but this dreaming is a biological necessity for humans.

Any time someone who claims that they never dream is brought into a lab
and hooked up to an EEG system,

a system to monitor their sleep within about 90 minutes of dozing off,
they exhibit REM.

Upon waking, they're usually pleasantly surprised
to realize that they do have dreaming experiences.

They just don't remember it, Perhaps never have remembered it.

But it's still happening almost every night.

There are a few exceptions to this, I should note.

If you take depressants like barbiturates
or large amounts of alcohol on a consistent basis before sleeping,

the REM process can be blocked entirely.

This can lead to a variety of health problems.

Actually, lack of dreaming might not come to mind
as the first of these health problems.

When patients stop taking the medication and try to sleep, they
periodically experience long, intense and sometimes nightmarish dreams.

This can be a problem in in and of itself.

But relevant to our discussion here, it seems that the brain
wants to have a certain amount of REM sleep each night

if it's starved of that phase of activity for an extended period.

For instance, due to one of these pharmaceutical interventions,
when the impediment to REM is removed,

it seems that the brain demands
a large amount of REM sleep to make up for lost time.

REM sleep seems to be an important part of our neurophysiology.

But what's it for?

It's worth noting we aren't the only animals who exhibit this.

If you have a dog, you've almost certainly seen him or her
twitching and yelping quietly in a dreamlike state.

All mammals, it turns out, exhibit a sleep cycle similar to humans.

There's even some evidence that ants engage in an analog of REM sleep.

Essentially, every creature
with a complex nervous system does this. Why?

One of the best explanations has to do with memory.

Many people report having dreams
about recent salient events in their lives.

This has led several researchers to a prediction
that REM sleep is responsible for somehow shoring up the long term

memories that we've formed over the course of a day, imprinting them
such that they'll remain more durable and accurate.

This is an empirical question. Of course we can test this.

We can run an experiment.

We can test the extent to which REM sleep is responsible for memory.

Perhaps the easiest, most obvious experiment
would be to just prevent someone from having any REM sleep.

A simple procedure might involve teaching someone something,

some set of information that they're then responsible
for recalling later, after they've had a night of sleep.

The experimenter would then

have the participants sleep in the lab with an EEG hooked up to monitor
When that REM sleep occurs.

Whenever it does, the experimenter would wake them up and stop the REM
to prevent the REM from ever happening.

If REM sleep is important to memory,
then reduced REM sleep should mean reduced memory.

Right. So this experiment works.

If you wake someone up seven or eight times during the night stopping
their REM sleep, they are really pretty bad at recalling information.

They're also, I should note, really tired
and probably more than a little annoyed at the experimenter.

Hopefully it's obvious that this is a problematic experiment.

As I've described it, we've removed the REM sleep for sure,
but also a lot of sleep in general.

Based on this, we can't be really sure that it's the REM that matters.

The best studies on this topic use what's called a yoked design,
in which two participants sleep in two adjacent labs.

Both are taught the same information and both are tested
the same way the following day.

One of these two sleepers is randomly assigned to the no REM condition.

He or she is the one whose REM indicates when both sleepers are woken.

So both participants are woken and annoyed an equal number of times
at the same time, actually throughout the evening.

On some occasions the control sleeper might actually be dreaming
at the same time as the no REM sleeper.

But there will be some other times
when this other sleeper is allowed to dream.

Thus, if dreaming is important for memory,
then the REM sleeper should do better on the test.

Different versions of this study have been repeated
dozens of times actually.

In general, REM sleep has been found to be important for memory.

This might not be the only role for REM sleep,
but the evidence is strong that when we engage in

REM sleep, we're doing something
that promotes the effectiveness of our long term memory.

With this in mind, it's often good advice to sleep prior
to taking some exam.

If you're planning, for instance, to sleep and study between now
and when you're going to take a test,

it's probably a good idea to do the studying first and then the sleep
as opposed to sleeping and then studying in the morning.

Doing it in the opposite order.

Sleeping after learning
seems to play a role in cementing the knowledge in your mind.

A few recent studies have suggested that

this sleeping after studying is most important, with topics
where you plan to use the information in an abstract way.

For instance, if you're studying calculus, theorems and proofs, you'll
be asked on an exam to do more than simply recall this information.

On most exams, you'll be expected to apply that information
to novel problems that you've never seen before.

The test.

It's in this situation that the sleep, the REM sleep in particular
seems to play its most important role.

If you're just memorizing a vocabulary list,
you'll be asked to recite from memory.

Then sleep is still a good idea before the test,
but it seems to play a smaller role in determining your performance.

The one other topic of note in this section
is the role that nutrition plays in promoting memory.

The brain is certainly an organ that benefits from a varied, nutrient
rich diet, just like any other part of your body.

There's also good evidence
that good circulation is important for good health.

Actually, it's been hypothesized
that it's the circulation that might be the important factor.

Mediating the exercise studies that I described before.

That is maybe it's not so much
the exercise that increases brain performance,

but just the extra oxygenated blood that your newly fit
heart and lungs can deliver to your brain.

So in general,

there's evidence to suggest that a diet that helps you to stay fit in
general is good for your memory and for your brain.

Beyond that, however, the evidence grows much thinner.

It's not hard to find ads for brain healthy foods and vitamin
supplements, fish oils, antioxidants, fiber rich fruits,

even caffeine have been associated with improved memory function
by at least one study.

The jury remains out,
however, on just how much or how often these supplements are needed.

If your body is low on just about any nutrients, then a supplement of
that might help your body in general and might help your memory.

This makes these studies very hard to interpret.

One of the largest observed effects I've seen on nutrition and memory
found that eating breakfast enhances mental function.

It didn't seem to matter what you ate as long as you ate something.

In retrospect, of course, this makes total sense.

If your body lacks basic nutrients in the morning, which it typically
does, then providing those nutrients will boost memory performance

for the moment.

I would suggest proceeding with caution.

Nutrition certainly matters for your physical, biological brain,
but I would urge against investing

in megadoses of some particular substance
just because it's been linked to memory function.

Just because a small amount results in a small improvement in memory
doesn't mean at all that a large amount will produce

a large improvement, and a large dose of just about anything
might produce unpleasant side effects in the process.

In this session,

I've described how your whole brain is involved in remembering things
not just the hippocampus, not just particular parts of the brain.

To have a good memory functioning at its peak.

You need to keep the whole brain healthy.

I've also talked about the science behind studies of exercise,
sleep and nutrition and how they relate to mental function.

In a sense, science
here is telling you what your mother probably told you.

Eat a balanced diet,
get out for some vigorous exercise and get a good sleep.

Good night's sleep just about every night.

If you do, then your brain will remember that you did
and hopefully remember to send a card on Mother's Day

to you next time.